There is a desire in the industry for higher circuit density in microelectronic devices made using lithographic techniques. One method of achieving higher area density is to improve resolution of circuit patterns in resist films. The use of shorter wavelength radiation (e.g. deep UV-220 to 280 nm) than the currently employed near and mid-UV spectral range (300 nm to 450 nm) offers the potential for improved resolution. However, with deep UV radiation, fewer photons are transfered for the same energy dose to achieve the same desired photochemical response. Further, current lithographic tools have greatly attenuated output in the deep UV spectral region. Therefore, there is a need in the art to develop resist materials which are more sensitive to radiation in deep UV.
Poly(bisalkyl)silanes and poly(methylphenyl)silane are known in the art for use as a resist e.g. in making bilayer photoresist, Miller et al., Materials for Microlithography, ACS Symposium Series 266, page 293, 1984. The bilayer resist comprises an imaging, oxygen plasma resistant polysilane layer over a planarizing polymer layer coated on a substrate. When the resist is imaged, the radiation causes photochemical degradation of the exposed polysilane into lower molecular weight material. Photochemical degradation is accompanied by a proportional amount of spectral bleaching which is used in the art to measure the degree of degradation. The degradation of the exposed polysilane enables wet development of a positive image with common organic solvents. The image is then transferred through the underlying polymer layer to the substrate by oxygen plasma development. However, current polysilanes lack sensitivity and require large radiation doses of 100 to 400 millijoules/cm.sup.2 for suitable imaging and therefore are generally less desirable for commercial use especially in deep UV. It is therefore an object of the present invention to provide improved photosensitive polysilanes for use as photoresist.
Other objects and advantages will become apparent from the following disclosure.